1. Field of the Invention
The present invention relates to a welding machine and a welding method, by which and in which cylinder members are connected together. Specifically, one cylinder member is inserted within another cylinder member and energy is applied to the outside cylinder member, around an outside diameter of the cylinder member, using an energy-applying unit(s), so that the cylinder members become welded together.
2. Description of Related Art
Generally, when multiple cylinder members are welded together around their peripheries, energy is applied to the cylinder members in a single direction using an energy source. An example is shown in FIG. 8. First, an inner cylinder member 201 having a columnar shape is press-fitted into an outer cylinder member 200 having a circular pipe-like shape. Then, a laser beam 211, generated by a laser generator, is focused on the outer cylinder member 200 using an optical head 210 disposed outside the outer cylinder member 200. Thus, the outer cylinder member 200 and the inner cylinder member 201 become welded to each other at a point of contact at an outer periphery while cylinder members 200 and 201 are rotated.
However, when both cylinder members are welded to each other by applying energy to both at only one position, a problem occurs. That is, relative thermal distortion is generated among a non-melted portion, a melted portion due to the applied energy, and a portion starting solidification. For this relative thermal distortion, both cylinder members are deformed from a pre-weld shape 220 shown in FIG. 9A to a post-weld shape 221 shown in FIG. 9B. As shown in FIG. 9B, both cylinder members are deformed in a direction perpendicular to an energy-applying direction, and each cylinder member is deformed to an elliptical shape when viewed in cross-section.
Here, elliptical-deformation processes will be described when the cylinder members are welded in the circular or circumferential direction by applying energy in a single direction using an energy source. Before welding, for example, when one cylinder member is press-fitted into and attached to another cylinder member, both cylinder members are deformed. Then, this deformation is made larger by relative distortion between an expanded portion and a contracted portion due to welding, and each cylinder member is deformed to an elliptical shape in its cross section. Even when the cylinder members are not deformed and substantially have a complete circular shape before welding as shown in FIG. 9A, they are deformed after welding as shown in FIG. 9B. The shape 220 substantially having a circular shape tends to deform to the shape 221 having an elliptical shape in a direction crossing the energy-applying direction at a weld-starting position. In FIGS. 9A and 9B, larger and smaller circles described with broken lines indicate the largest and smallest diameters among the welded and deformed portions, respectively.
Irrespective of deformation before welding, when welding is performed in an angle area from zero degrees to 90 degrees in a circular direction, the cylinder members are deformed to an elliptical shape due to thermal expansion, and an amount of deformation increases. When the welding proceeds to an angle of 180 degrees, the elliptical deformation is relieved by expansion due to welding progress in an angle area from 90 degrees to 180 degrees and by shrinkage due to solidification in the angle area from zero degree to 90 degrees. Then, the amount of the deformation is decreased. When the welding proceeds to an angle of 270 degrees, the relieved elliptical deformation is again enlarged by expansion due to welding progress in an angle area from 180 degrees to 270 degrees. When the welding proceeds to an angle of 360 degrees, the elliptical deformation is relieved by expansion due to welding progress in an angle area from 270 degrees to 360 degrees and by shrinkage due to solidification in the angle area from 180 degree to 270 degrees. Then, the amount of the deformation decreases. As the welding proceeds in the angle area, the amount of the deformation increases and decreases. The cylinder members are deformed to an elliptical shape due to welding. Even when the welding proceeds beyond 360 degrees and the same portion is welded many times, the above-described deformation process is repeated at the previously-welded portions. In a member requiring metal sealing, when the member is deformed by welding, sealing performance is degraded.
In FIGS. 9A and 9B, large and small circles shown with broken lines indicate the largest and smallest diameters among the welded and deformed portions, respectively. The shape 220, being substantially circular, tends to be deformed to the elliptical shape 221 in a direction crossing the energy-applying direction at a weld-starting position.
In order to restrict both cylinder members from being deformed due to the method where energy is applied to both in a single direction, the following method is considered. As shown in FIG. 10, energy is applied to both cylinder members at two positions simultaneously in directions opposing each other at 180 degrees. However, energy is applied to the outer and inner cylinder members 200 and 201 at two positions opposing each other in the radial direction, and both cylinder members are readily deformed at two positions. Therefore, both cylinder members are readily deformed in a direction perpendicular to the energy-applying direction. Accordingly, a shape 230, substantially having a complete circular shape before welding as shown in FIG. 11A, tends to be deformed to a shape 231 having an elliptical shape after welding, shown in FIG. 11B, in a direction crossing the energy-applying directions at weld-starting positions. In FIGS. 11A and 11B, large and small circles shown with broken lines indicate the largest and smallest diameters among the welded and deformed portions, respectively.
When foreign matter is mixed into a portion to be melted with applied energy, the foreign matter may be evaporated by the applied energy, so that pores are sometimes generated at the welded portion. When pores are generated at the welded portion, welding failure may occur.